The subject embodiment pertains to the art of printing systems and more particularly printing systems including a plurality of printing engines capable of operating in parallel for parallel or sequential printing of job portions. The preferred embodiments especially relate to a system and method for synchronizing relative operating positions of photoreceptor belts within the printing assembly to avoid undesirable belt seam positioning that can diminish system throughput efficiency.
Printing engines utilizing photoreceptor belts, as opposed to drums, must avoid using the portion of the belt comprising the seam because the seam, if used to store any image data, can mar the output image. In most engine printing systems, paper feeding systems will detect seam position to avoid lining up the paper with the seam. When such avoidance requires delaying the printing operation for the time period of printing a single page, such a wait is referred to as “skipping a pitch” and has a noticeable negative consequence on printing systems throughput efficiency. Adjusting the feed of the paper to assure avoidance of the seam is normally all that is needed in single print engine systems and is usually successful enough so that a pitch is hardly ever skipped.
A special problem exists in multiple print engine systems where a first printing engine (image output terminal or “IOT”) can be a presequential feeder to a second IOT. Of importance is that the second IOT be synchronized to the first IOT, i.e., that the second photoreceptor belt seam is synchronized to the first photoreceptor belt seam, to avoid the pitch skipping problems.
When such parallel printing assemblies are initially constructed, it is intended that the respective photoreceptor belts be of the same size (length) and that the motor speed for operating the belts of the IOTs are identical. In such cases, initial calibration is intended to avoid having to adjust the relative positions or operating speeds of the respective engines during operation, or that the feeding system can adjust positions of the documents during input to each engine to accommodate any throughput problems that may arise.
It is an operational objective that there is no delay in paper feed through the system so that throughput can always be maximized. Unfortunately the practical reality is that no two photoreceptor belts are exactly the same size, nor are their respective motors capable of running at exactly the same speed. The respective differences may be quite small, but over time, and the production of many print documents, the respective belts can become so out of synchronization that the conventional paper feed adjustment systems may not be capable of accommodating the phase feed differences and a pitch may have to be skipped.
Accordingly, there is a need for a system capable of monitoring position and phase relationships between respectively associated IOTs, their belts and their seams, so that whatever differences do exist, may be maintained within acceptable ranges to avoid the problems of skipping pitches and throughput delays.